Recently, liquid crystal display apparatuses are widely used as various display apparatuses such as display apparatuses for word processors, computers, navigation systems and the like. Moreover, the liquid crystal display apparatuses have been improved to have such a display quality that allows the liquid crystal display apparatuses to be used for color display.
Especially, liquid crystal display apparatus of active matrix type are mainly used. In the liquid crystal display apparatus of active matrix type, pixels are provided in matrix, and an active element such as a thin film transistor and the like is provided to each pixel. The active element functions as a switching element of the pixel to which the active element is provided.
A general liquid crystal display apparatus of active matrix type is provided with a first glass substrate and a second glass substrate. The first glass substrate is provided with scanning lines, gradation signal lines, switching elements, and pixel electrodes. The second glass substrate is provided with a black matrix, a color filter and a common electrode. The first and second glass substrates are so positioned as to face one another with a predetermined gap region therebetween. A liquid crystal material is filled in the gap. Then, a sealing material, which is cured (hardened) by application of heat or light, is applied around the first and second glass substrates. By using the sealing material, the first and second glass substrate are sealed. Voltages between the pixel electrodes and the common electrode are controlled pixel by pixel so as to perform gradation display in which gradation of each pixel is controlled.
The high cost of such liquid crystal display apparatus has not been reduced because of its complicated manufacture and large number of parts. Reduction in retail price of the liquid crystal display apparatus is necessary for obtaining a wider market. In view of this, various arts have been suggested to reduce a cost of the color filter, which is one of most expensive constituent elements of the liquid crystal display apparatus.
In general, the pigment dispersing method is used for manufacturing the color filter. In the pigment dispersing method, a filter pattern is formed by a photo process. In the pigment-dispersing method, specifically, a photosensitive resin in which a pigment is dispersed is wholly applied on a surface of the substrate by the spin-coating or the like. A film of the photosensitive resin is developed by performing pattern-exposure of the film to ultra violet radiation. Thereby, a filter pattern of one color is formed. The film is developed several times in this manner so as to form a color filter layer including a black matrix.
In the pigment dispersing method, a majority of the photosensitive resin in which the pigment is dispersed is removed in the development for forming filter patters of each color. Therefore, the pigment dispersing method has a high material cost. The high material cost hinders the reduction in the manufacturing cost of the color filter.
Recently, a method of manufacturing a color filter by using the ink-jet method is suggested for reduction in the material cost and the number of steps in manufacturing the color filter. For example, U.S. Pat. No. 6,399,257 B1 suggests such a method.
With reference to FIGS. 15(a) to 15(f), the method of manufacturing the color filter disclosed in U.S. Pat. No. 6,399,257 B1 is explained below. Note that FIGS. 15(a) to 15(f) illustrate the following steps a to f, respectively
In the step a, a light shielding layer 102 (black matrix) having opening sections 102a is formed on a substrate 101. The shielding layer 102 is constituted of light shielding members patterned in lines or in grid. The shielding layer 102 is formed by patterning a photosensitive black resin layer or the like by the photolithography method. Here, the light shielding layer 102 is made of a black resin and has a large thickness, so that the light shielding layer 102 functions as a portion in later-described application of a curing ink. Note that the shielding layer may be formed by another method, for example, thermal imaging process (LITI method) disclosed in EP 1,226,974 A1.
In the step b, a photosensitive layer 103 is formed overall on a surface of the substrate 101 on which the light shielding layer 102 are formed. The photosensitive layer 103 is a layer that becomes hydrophilic or more hydrophilic by radiating light thereon. Preferably, the photosensitive layer 103 contains at least one of TiO2, SnO2, ZnO, WO3, SrTiO3, Bi2O3, and Fe2O3, as a photosensitive compound. When light is radiated on the photosensitive layer 103 containing at least one of those compounds, electrons and pores are exited by the radiation of the light. The excited electrons and pores react with water and oxygen that is adsorbed to a surface of the photosensitive compound, thereby producing active oxygen. As a result, that area of the photosensitive layer 103 on which the light is radiated becomes hydrophilic. On the other hand, metal oxides such as the photosensitive compounds are, by nature, hydrophobic and oil-repellant. Thus, that area of the photosensitive layer 103 on which the light is not radiated does not become hydrophilic. Thus, ink is likely repelled on that area of the photosensitive layer 103 on which the light is not radiated. Therefore, in applying the curing ink by using the ink-jet method as described later, a non-light-radiated area (that is, non-hydrophilic regions) between each adjacent light-radiated area (that is, hydrophilic region) repels the ink thereby having color mixing prevention function. Thus, it is possible to prevent ink of different color from mixing with each other.
Specific examples of the methods of forming the photosensitive layer 103 using the photosensitive compound are (a) a sintering method in which the photosensitive compound is sintered on the substrate by applying a high temperature (a temperature higher than crystallization temperature of the photosensitive compound), and (b) a calcining method in which a composition prepared by dispersing alkoxysilane and the photosensitive compound in a solvent such as alcohol or the like is applied on the substrate 101 and heated so as to form a film.
In the sintering method, it is necessary to apply a high temperature not less than 400° C. In case the light-shielding layer 102 and the like, which is essentially made of a resin material, are formed on the substrate 101, there is a possibility that the light-shielding layer 102 is deteriorated by the high temperature application. Thus, the sintering method is not so preferable in such a case. Moreover, even if the light-shielding layer 102 is made of a metal material such as chromium or the like, the sintering method is not so preferable because the high temperature application likely causes size inaccuracy of the light shielding layer 102. Therefore, the calcining method is preferable in which the composition is applied and calcined because the calcining method uses a lower temperature.
The photosensitive layer 103 thus formed becomes more hydrophilic by the pattern-exposure that causes water molecules and the like to be adsorbed to the light radiated areas. As to wavelength of the light for use in the pattern-exposure, light of relatively short wavelength out of the ultraviolet region should be used for some photosensitive compounds, whereas visible light of relatively long wavelength may be used for some photosensitive compounds. Thus, a wavelength most suitable for the photosensitive compound to be used may be arbitrarily selected.
Examples of the method of applying the composition so as to form the photosensitive layer 103 are: spin coating, roll coating, bar coating, spray coating, dip coating, and the like.
A thickness of the photosensitive layer 103 is preferably in a range of 0.01 μm to 10 μm, and more preferably in a range of 0.01 μm to 5 μm.
In step c, the photosensitive layer 103 is exposed to the light directed thereto from below the substrate 101 (the light is directed to the photosensitive layer 103 via the substrate 101), so as to form hydrophilic regions 104 in the areas that are exposed to the light. The hydrophilic regions 104 are the areas that become hydrophilic or more hydrophilic by the radiation of the light. The areas that are not exposed to the light are less hydrophilic. Thus, the areas that are not exposed to the light are referred to as non-hydrophilic regions 105 here for easy explanation. The photosensitive layer 103 is formed on the light-shielding layer 102. Thus, the exposure of the photosensitive layer 103 can be performed with the light-shielding layer 102 used as a mask. It is preferable to form color sections (sections that are to be colored) so that the color sections have a larger area than the opening sections 102a, in order to prevent the color filter from having a white spot (an uncolored spot that is caused in a border section between the color section and the light-shielding layer). In view of this, it is necessary that the part of the photosensitive layer 103 which is to be exposed be larger than the opening sections 102a in the light shielding layer 102. Specifically, it is preferable to use scattering light so as to radiate in the exposure. Alternatively, for example, it is also effective that over exposure is carried out so as to cause the reaction in a larger area.
Note that, here, the photosensitive layer 103 is exposed to the light directed thereto from below the substrate 101. However, it may be arranged such that the photosensitive layer 103 is exposed to the light directed thereto from above the substrate while using a photo mask. In this case, in order to prevent the formation of white spots, it is preferable that the mask used has an opening section wider than the opening section 102a of the light-shielding layer 102. Specifically, it is preferable that the areas that are not exposed are formed on parts of the light-shielding layer 102 whose edges are located inner from edges of the opening sections 102a of the light-shielding layer 102a by 3 μm or more.
The pattern exposure may be carried out in stripe (line) or in grid, as shown in FIGS. 16(a) and 16(b). FIG. 16(a) illustrates a case in which the pattern exposure in stripe is carried out. In this case, the light-shielding layer 102 is provided with the opening sections 102a for respective pixels. Color sections 107 in a stripe shape are continuously aligned in a row direction. FIG. 16(b) illustrates a case where the pattern-exposure in matrix is carried out. In this case, the matrix of the pattern-exposure corresponds to locations of the opening sections 102a of the light-shielding layer 102.
In step d, curing ink 106 (ink that can be cured) is applied on the hydrophilic regions 104 by the ink-jet method in accordance with a predetermined color pattern. In general, for making a color filter, the curing ink 106 is ink of three colors, namely, R, G, and B (Red, Green, and Blue).
It is preferable that the curing ink 106 used here contains polymers, oligomers or the like as a binder component (a bridging component to perform bridging by heat application or light radiation). Such polymers, oligomers, and the like may be constituted by solely polymerizing a monomer constituted of a structural unit represented by the following chemical formula (1), or by copolymerizing the monomer with another vinyl monomer. Note that R1 and R2 in chemical formula (1) are substituents and may be different from each other.

The monomer constituted of the structural unit represented by chemical formula (1) may be, but not limited to, N-methylolacrylamide, N-methoxymethylacrylamide, N-ethoxylmethylacrylamide, N-isopropoxylmethyacrylamide, N-methylolmethacrylamide, N-methoxylmethylmethacrylamide N-ethoxymethylmethacrylamide, and the like. The monomer may be polymerized solely, or copolymerized with another vinyl monomer. The another vinyl monomer may be, but not limited to, (i) acrylic acid, (ii) methacrylic acid, (iii) ester acrylic acids such as methyl acrylic acid, ethyl acrylic acid, and the like, (iv) ester methacrylic acids such as methyl methacrylic acid, ethyl methacrylic acid, and the like, (v) vinyl monomers containing a hydroxyl group, such as hydroxymethylmethacrylate, hydroxyethylmethacrylate, hydroxylmethylacrylate, hydroxylethylacrylate, and the like, (vi) other compounds such as styrene, α-methyl styrene, acrylamide, methacrylamide, acrylonitril, allylamine, vinylamine, aceticamine, vinylpropionate, and the like.
Moreover, a molecular weight of a major constituent of the compound (binder component) is preferably in a range of 500 to 50000, more preferably in a range of 1000 to 20000, considering that the compound should be jetted out (applied, sprayed) by the ink-jet method. Furthermore, content of the compound in the ink is preferably in a range of 0.1% by weight to 15% by weight, more preferably in a range of 1.0% to 10% by weight.
Furthermore, the curing ink 106 contains a color material, which may be of dye type or pigment type.
Moreover, (i) the bubble-jet type (“bubble jet” is a trademark of Canon, Inc.) in which an electric-heat converter as an energy generating element, (ii) piezo jet type in which a piezoid is used, (iii) and the like method may be used as the ink-jet method. Color section and color pattern of the ink-jet method may be arbitrarily set.
In step e, the curing ink 106 is cured by a necessary process, that is, heat application or light radiation. Thereby, color sections 107 of R, G and B are formed.
In step f, according to need, a protective layer 108 is formed. The protective layer 108 may be (i) a resin layer that is made of a photo-curing type resin, a thermal curing type resin, a resin that is cured by both light and heat, (ii) an inorganic film that is formed by deposition, sputtering, or the like, (iii) or the like, provided that the color filter having the protective layer 108 is transparent, and has enough tolerance to undergo ITO (Indium-Tin Oxide) film (transparent electrode) formation process, and alignment layer formation process.
Incidentally, in the manufacturing method disclosed in U.S. Pat. No. 6,399,257 B1, the light-shielding layer 102, which has the portioning function in applying the curing ink, functions as a black matrix of the color filter. The light-shielding layer 102 is grid-shaped (patterned in matrix), as shown in FIGS. 16(a) and 16(b). Hereinafter, the light-shielding layer 102 is referred to as a black matrix 102.
When the curing ink 106 is applied, by the ink-jet method, onto the substrate 101 on which the black matrix 102 of the grid shape is formed, an amount of the curing ink 106 to be applied into each opening section 102a is dependent on how many droplets are jetted into each opening section 102a. This is because, in the black matrix 102 of the matrix shape, the curing ink 106 thus applied does not flow from one opening section 102a to another opening section 102a. Thus, the amount of the curing ink 106 to be applied into each opening section 102a is determined by how many droplets are jetted into each opening section 102a 
Moreover, the amount of the curing ink 106 to be applied in each opening section 102a determines color density in each opening section 102a. Thus, in order to prevent uneven color densities among the opening sections 102a, it is necessary to control the jetting such that the substantially same number of the droplets of the curing ink 106 are jetted into each opening section 102a. 
However, in reality, it is very difficult to control the jetting (application of ink) as such in the ink-jet method. As a result, there is such a problem that the color densities are highly uneven among the opening sections 102a when the ink-jet method is used for the black matrix 102 of the grid shape as shown in FIGS. 16(a) and 16(b).
FIG. 17 illustrates a black matrix 112 having such a pattern that each opening section 112a is not partitioned in a column direction. On contrary to the black matrix 102 of the grid shape as shown in FIGS. 16(a) and 16(b), it is easier to apply the curing ink 106 in even amounts in each opening section 112a in the black matrix 112 as shown in FIG. 17. The amount of the curing ink 106 to be applied in each opening section 112a of the black matrix 112 is much greater than the amount of the curing ink 106 to be applied in each opening section 102a of the black matrix 102. Thus, in the black matrix 112, it is easier to suppress the unevenness among the opening sections 112a in terms of the amount of the curing ink 106 to be applied therein. For example, in case of a color filter for a XGA class liquid crystal display apparatus, the amount of the curing ink 106 to be applied in each opening section 112a is about 768 times greater than that in each opening section 102a. 
Therefore, compared with the black matrix 102, it is easier in the black matrix 112 to suppress the unevenness among cells in terms of the color density.
However, the inventors of the present invention found that the following problems arise in the black matrix shown in FIG. 17.
In applying the curing ink 106 by using the ink-jet method, the substrate 101 is scanned by using an ink jet head with a predetermined relative velocity Vh. Moreover, the curing ink 106 is jetted out from the ink jet head at a jetting-out velocity Vv. Therefore, a droplet of the curing ink 106 is hit at the substrate 101 at a resultant velocity Vt, which is a resultant velocity of the relative velocity and the jetting out velocity Vv, as shown in FIG. 18.
When the droplet 106a hits the substrate 101 at the resultant velocity Vt, the liquid droplet 106a thus is spread widely from a point at which the droplet 106a hits. If the resultant velocity Vt, especially, the relative velocity Vh is large, the curing ink 106 is so spread that, as shown in FIG. 19, the curing ink 106 is thick upstream and thin downstream of the relative velocity Vh. As a result, the color sections made of the curing ink 106 have uneven thickness, thereby causing uneven color density.
Moreover, if the resultant velocity Vt, especially, the relative velocity Vh is large, a speed of spreading the curing ink 106 is fast. In this case, there is a possibility that part of the curing ink 106 flows over the black matrix 112 that is the partition, and flows over even the non-hydrophilic region 105, so as to reach the opening section 112a adjacent thereto. This causes color mixing between adjacent color sections 107.
One solution avoid such problem is to reduce the relative velocity. However, the reduction of the relative velocity lowers throughput of the applying step of the curing ink 106, thereby reducing productivity of the color filter.
That is, when the art used conventionally is adopted in the ink jet method that is effective in reducing the material cost and the number of steps, it is not possible to solve the problem of deterioration of the property of the color filter, without deteriorating high productivity.
Further, the inventors of the present invention found that the color sections 107 tend to be thicker toward edge parts and thinner in a middle part (longitudinally) with respect to a vertical direction in FIG. 17, the color sections 107 formed by applying the curing ink 106 onto the substrate on which the black matrix 112 as shown in FIG. 17 is provided. Because the edge parts are where the flow of the curing ink ends, ambient vapor concentration of a vaporized solvent is less around the edge parts and more around the middle. Thus, the curing ink 106 dries at a higher drying rate in the edge parts compared with in the middle part. As a result, the curing ink 106 flows from the middle part, where the curing ink 106 dries slower, toward the edge parts. This phenomenon causes unevenness in the color density between the middle part and edge parts in the color filter.
Note that the problem is not limited to the production of the color filter, but is common in the manufacturing process including the step of forming a film by applying a film material by using the ink-jet method.